diff --git a/ble.cabal b/ble.cabal
--- a/ble.cabal
+++ b/ble.cabal
@@ -1,9 +1,9 @@
--- This file has been generated from package.yaml by hpack version 0.17.0.
+-- This file has been generated from package.yaml by hpack version 0.17.1.
 --
 -- see: https://github.com/sol/hpack
 
 name:           ble
-version:        0.4.1
+version:        0.4.2
 synopsis:       Bluetooth Low Energy (BLE) peripherals
 description:    This package provides a Haskell API for writing Bluetooth Low Energy peripherals.
 stability:      alpha
@@ -114,7 +114,7 @@
   hs-source-dirs:
       examples
   default-extensions: AutoDeriveTypeable ConstraintKinds DataKinds DefaultSignatures DeriveFoldable DeriveFunctor DeriveGeneric DeriveTraversable FlexibleContexts FlexibleInstances FunctionalDependencies GADTs KindSignatures MultiParamTypeClasses OverloadedStrings RankNTypes ScopedTypeVariables TypeFamilies TypeOperators
-  ghc-options: -Wall
+  ghc-options: -Wall -threaded
   build-depends:
       base >= 4.8 && < 4.10
     , bytestring >= 0.10 && < 0.11
@@ -145,7 +145,7 @@
   hs-source-dirs:
       examples
   default-extensions: AutoDeriveTypeable ConstraintKinds DataKinds DefaultSignatures DeriveFoldable DeriveFunctor DeriveGeneric DeriveTraversable FlexibleContexts FlexibleInstances FunctionalDependencies GADTs KindSignatures MultiParamTypeClasses OverloadedStrings RankNTypes ScopedTypeVariables TypeFamilies TypeOperators
-  ghc-options: -Wall
+  ghc-options: -Wall -threaded
   build-depends:
       base >= 4.8 && < 4.10
     , bytestring >= 0.10 && < 0.11
diff --git a/examples/HeartRate.hs b/examples/HeartRate.hs
--- a/examples/HeartRate.hs
+++ b/examples/HeartRate.hs
@@ -90,16 +90,22 @@
 heartRateMeasurement :: AppState -> CharacteristicBS 'Local
 heartRateMeasurement appState
   = "00002a37-0000-1000-8000-00805f9b34fb"
-     & readValue ?~ fmap heartRateToBS (liftIO . readIORef $ currentHeartRate appState)
+     & readValue ?~ fmap heartRateToBS (liftIO readV)
      -- Even though we add a @writeValue@, this does not mean that the
      -- characteristic is writable (for that, we would need to add the CPWrite
      -- property to it). Instead, we can use the writeValue internally to
      -- update the value and send notifications each time the value is changed.
      & writeValue ?~ encodeWrite (liftIO <$> write)
-     & properties .~ [CPNotify, CPRead]
+     & properties .~ [ CPNotify, CPRead, CPWrite ]
   where
+    readV = do
+      putStrLn "Reading value"
+      readIORef $ currentHeartRate appState
+
     write v = do
+      putStrLn "Received value"
       writeIORef (currentHeartRate appState) v
+      putStrLn "Wrote value"
       return True
 
 heartRateToBS :: Word8 -> BS.ByteString
diff --git a/package.yaml b/package.yaml
--- a/package.yaml
+++ b/package.yaml
@@ -1,5 +1,5 @@
 name:                ble
-version:             0.4.1
+version:             0.4.2
 synopsis:            Bluetooth Low Energy (BLE) peripherals
 description:         >
     This package provides a Haskell API for writing Bluetooth Low Energy
@@ -123,6 +123,7 @@
   hrs:
     main:            HeartRate.hs
     source-dirs:     examples
+    ghc-options:     -threaded
     dependencies:
       - ble
       - hslogger
@@ -135,5 +136,6 @@
   hrs-client:
     main:            HeartRateClient.hs
     source-dirs:     examples
+    ghc-options:     -threaded
     dependencies:
       - ble
diff --git a/src/Bluetooth/Internal/HasInterface.hs b/src/Bluetooth/Internal/HasInterface.hs
--- a/src/Bluetooth/Internal/HasInterface.hs
+++ b/src/Bluetooth/Internal/HasInterface.hs
@@ -204,10 +204,12 @@
 
       writeVal = case char ^. value . writeValue of
         Just w -> Method (repMethod $ go w)
-                          "WriteValue" ("arg" :> Done) ("rep" :> Done)
+                          "WriteValue" ("arg" :> "options" :> Done) ("rep" :> Done)
         Nothing -> Method (repMethod notSup) "WriteValue" Done Done
         where
-          go writeTheVal newVal = do
+          go :: (BS.ByteString -> Handler Bool)
+             -> BS.ByteString -> CharacteristicOptions -> MethodHandlerT IO Bool
+          go writeTheVal newVal _opts = do
             res <- handlerToMethodHandler $ writeTheVal newVal
             nots <- liftIO $ readMVar $
               characteristicIsNotifying (char ^. value . uuid)